Fluids produced from wells typically contain a complex mixture of components including aliphatic hydrocarbons, aromatics, hetero-atomic molecules, anionic and cationic salts, acids, sands, silts and clays. The nature of these fluids, combined with the severe conditions of heat, pressure, and turbulence to which they are often subjected, are contributing factors to the formation and deposition of unwanted contaminants, such as scales, salts, paraffins, corrosion, bacteria and asphaltenes in oil and/or gas production wells.
Such unwanted contaminants typically restrict the movement of fluids in production piping and further potentially plug flow paths of fluids (including reservoir flow paths). For instance, common mineral scales such as calcium carbonate, calcium sulfate, or barium sulfate often precipitate from produced water and create blockages in flow paths in production tubulars. The formation and deposition of such unwanted contaminants reduce well productivity, and, in some cases, completely blocks the tubing.
Treatments to remove deposits and inhibit the formation of unwanted deposits include the use of various mechanical preventative techniques such as scrapers or reamers and chemical treatment agents such as inhibitors, acids and converters. While mechanical tools are effective when the tubular is at an approximate 180° to the point of entry (as gravity helps pull the treatment device into the well), they have limited effectiveness when the tubular being treated is deviated, as in a horizontal well or “S” shaped configuration. The flexibility of mechanical tools makes it difficult to push a long distance past a severe deviation or multiple deviations. Chemical prevention or remedial techniques can be effective if the treatment can be delivered reliably to the target location and in sufficient quantity to address the issues.
Chemical treatment agents may be delivered to unwanted deposits by the technique of “downhole squeezing” wherein a slug of a well treatment composition is injected into the annulus of the well, using a pre-flush, squeeze, and over flush treatment before the well can be returned to normal function. This technique requires large volumes of treatment and flush fluid in horizontal wells with a large area of perforated interval. Further treatments are typically required as the chemical residual is depleted, once again requiring large volumes of flush and treatment into the well. Such treatment methods are typically inefficient in horizontal wells because it is difficult to ensure the treatment is delivered to all the intended area. Further, the flush and chemical additives often require large pumps and holding tanks which can add significant costs to the application.
Solid chemical additives in the form of a slurry are further often used. This type of treatment is effective in vertical wells but requires a flush to aid in delivery of the treatment agent to the bottom of the well. In a deviated well such as a horizontal well or well with multiple deviations such as an “S” shaped completion, it is important that the slurry mass not be too heavy in order for the flush to be carried past the deviation. If the density of the slurry is too high, the slurry just settles beyond the deviation.
Capillary tubing lengths are frequently installed in wells to aid in delivery of a chemical treatment. This technique is effective in its intended function but is expensive and requires specialized equipment to install. Further, capillary tubing may not be able to extend to great depths if the deviation angle is severe or the piping extends far beyond the bend.
While solid additives have been added to the well during the completion stage, this technique has only been proven to be an effective delivery method in new wells when the opportunity to spot the chemical additive is available.
Alternative treatment methods have therefore been sought for introducing solid well treatment agents into producing oil and/or gas wells and especially in those where tubing is deviated or contains multiple deviations.